Chemical Reaction Hazard Testing

Uncompromising safety standards and chemical process optimization

The consequences of runaway exothermic chemical reactions can be devastating. Runaway reactions at Bhopal and Seveso serve to highlight the lasting impression created by such events and the indelible smudge on the reputation of the operating companies involved. When working with any manufacturing process it is always necessary to establish the hazards associated with its operation.

The understanding of chemical reactions and material reactivity is a critical element of safe processing as exothermic chemical processes are abundant in manufacturing processes. Often these reactions are inherent in the transformation we are undertaking (e.g. the conversion of styrene to polystyrene) – on other occasions these may be unintended reactions which are not part of our processing plan (e.g. decomposition of a material due to contamination or over-temperature exposure).

The identification, assessment and characterization of both intended and, more importantly, unintended exothermic reactions, are critical for ensuring the safe scale-up and operation of a chemical process. This often involves the employment of a strategy to assess reaction hazards and thermally unstable substances to most foreseeable plant situations.

Our preventive methodology, designed to be a cost-effective mechanism for assessing all processes, encompasses chemical reaction hazard assessments. We have state-of-the-art laboratory technology and extensive experience in chemical process development and optimization field. We can bring fresh, practical approach to old processes and have the resources available to study and provide speedy solutions.

Rigorous chemical reactions tests for transformational impact

It should be noted that when processing exothermic chemical reactions including thermally unstable substances and mixtures the hazard comes from pressure generation. Pressure can be generated in a closed vessel (or inadequately vented vessel) from:

These modes of pressure generation can arise from the desired reaction, a significant side reaction, or a secondary decomposition reaction. Identification of how pressure generation occurs is critically important for ensuring safety.

Background on selected methodologies

Screening Evaluation: The CHETAH program (The ASTM program for Chemical Thermodynamic and Energy Release Evaluation) is a unique tool for predicting both thermochemical properties and certain “reactive chemical hazards” associated with a pure chemical, a mixture of chemicals or a chemical reaction. CHETAH is useful for classifying materials for their ability to decompose with violence, for estimating heats of reaction or combustion, and for predicting lower flammable limits.

Differential Scanning Calorimetry (DSC): DSC is a method for thermal analysis using small samples of a few milligrams (micro-thermal analysis). Since DSC works on a micro scale using only a few milligrams of substance, it is possible to investigate highly exothermic processes under extreme conditions without any risk. The relatively small sample quantities used in DSC ensure sufficient temperature homogeneity within the sample and thus even high heat outputs can be measured quantitatively. In addition, the duration of an experiment in the scanning mode is only several hours, making the DSC technique a very rapid and powerful method for screening purposes.

Carius Tube with End Gas Analysis: Carius tube is a screening tool for thermal stability screening to search for exothermic activity and gas generation. Carius tube screening tests can detect exothermic activity such as the onset temperatures, identify pressure effects such as the onset of permanent gas generation and ultimately discern the quantity of gas generated during the test. The permanent gases generated can be analyzed by various analytical techniques such as GC-MS and GC-FID.

Accelerating Rate Calorimeter (ARC): The ARC is an automated laboratory instrument, which aids in experimentally determining the time, temperature, and pressure relationships of any exothermal reaction in a confined adiabatic environment. The data produced by the ARC can be applied to the evaluation of thermal and pressure hazard potentials of reactive chemicals and can be used for specifying plant protection measures including emergency relief system designs using DIERS technology.

Reaction Calorimetry (Mettler RC1): The Mettler RC1 reaction calorimeter is a computer controlled laboratory reactor that balances heat and mass flows. It is an excellent tool for studying the thermal characteristics of the desired reactions and for assuring safe process performance. RC1 data provides information such as energy of reaction, specific heat, adiabatic temperature rises and heat transfer coefficients. RC1 can be used for process development and optimization by studying the behavior of chemical processes in relation to changing process parameters, such as temperature, dosing, stirring, concentration and catalyst.

Adiabatic Pressure Dewar Calorimeter: This instrument enables plant-scale runaway reactions to be directly simulated in the laboratory. In addition, the Dewar calorimeter ensures direct simulation of reactors up to 25 m3, yields highly accurate test data and an accurate representation of multi-phase reaction mixtures, can be run batch, semi batch or gaseous batch and is a highly economic solution for combining process safety and development studies. The data from a Dewar experiment can be used for specifying plant protection measures including emergency relief system designs using DIERS technology.

Vent Sizing Package 2 (VSP2™): The Vent Sizing Package was originally developed during the DIERS project in the mid-1980s to collect data for vent sizing calculations on runaway exothermic reactions and decomposition; it was later commercialized as the VSP2™. Unlike the Adiabatic Dewar and ARC systems, which use thicker wall test cells to withstand high pressures, the 120 cm3 VSP2™ test cells are thin walled with a lower phi factor. This unit is one of the most well-known adiabatic calorimeters in the world and is particularly popular in the USA for the study of runaway reactions.